Bragg grating pressure sensor for industrial sensing applications

• US 6,776,045 B2
• Filed: 11/08/2001
• Issued: 08/17/2004
• Est. Priority Date: 12/04/1998
• Status: Expired due to Term

• Current Assignee: Cidra Corporate Services, Inc.
• Original Assignee: Cidra Sarl (Nordic Cultural & Educational Foundation)
• Inventors: Davis, Michael A., Kersey, Alan D., Fernald, Mark R., Bailey, Timothy J., Putnam, Martin A., Sanders, Paul E., Dunphy, James R., Wright, Christopher J., Brucato, Robert N., Sullivan, James M., Miller, Matthew B.
• Primary Examiner(s): Hirshfeld, Andrew H.
• Assistant Examiner(s): Ferguson, Marissa
• Application Number:
  US10/007,735
• Publication Number:
  US 20020154860A1
• Time in Patent Office: 1,013 Days
• Field of Search: 737/05, 737/08, 738/00, 385/12, 385/13, 385/51, 385/78, 385/96, 385/43, 356/477, 356/478, 250/231.19, 250/227.14, 250/227.17
• US Class Current: 73/705
• CPC Class Codes: G01L 11/025 using a pressure-sensitive optical fibre

Abstract

A fiber grating pressure sensor for use in an industrial process includes an optical sensing element 20,600 which includes an optical fiber 10 having a Bragg grating 12 impressed therein which is encased within and fused to at least a portion of a glass capillary tube 20 and/or a large diameter waveguide grating 600 having a core and a wide cladding and which has an outer transverse dimension of at least 0.3 mm. Light 14 is incident on the grating 12 and light 16 is reflected from the grating 12 at a reflection wavelength λ1. The sensing element 20,600 may be used by itself as a sensor or located within a housing 48,60,90,270,300. When external pressure P increases, the grating 12 is compressed and the reflection wavelength λ1 changes. The shape of the sensing element 20,600 may have other geometries, e.g., a “dogbone” shape, so as to enhance the sensitivity of shift in λ1 due to applied external pressure and may be fused to an outer shell 50. A temperature grating 270 may be used to measure temperature and allow for a temperature-corrected pressure measurement. The sensor may be suspended within an outer housing 112, by a fluid, spacers, or other means. The sensor may also be combined with an instrument, an opto-electronic converter and a controller in an industrial process control system.

Claims

1. An industrial process control system for controlling a process pressure of a fluid moving in a pipe, said control system comprising:

a pressure sensor disposed within said pipe in fluid communication with said fluid, said pressure sensor comprising;

an optical sensing element, having at least one pressure reflective element disposed therein, said pressure reflective element having a pressure reflection wavelength;

said sensing element being axially strained due to a change in external pressure, said axial strain causing a change in said pressure reflection wavelength, and said change in said pressure reflection wavelength being indicative of said change in pressure; and

at least a portion of said sensing element having a transverse cross-section which is contiguous and made of substantially a single material and having an outer transverse dimension of at least 0.3 mm;

wherein said pressure sensor provides a pressure signal indicative of said process pressure of said fluid; and

a processor that provides a control sianal, in response to the pressure signal, to a device that controls a parameter that effects the process pressure of the fluid within the pipe.

2. The industrial process control system of claim 1 wherein said sensing element comprises:

an optical fiber, having said reflective element embedded therein; and

a tube, having said optical fiber and said reflective element encased therein

along a longitudinal axis of said tube, said tube being fused to at least a portion of said fiber.

3. The industrial process control system of claim 2 wherein said tube is fused to said optical fiber where said reflective element is located.

4. The industrial process control system of claim 2 wherein said tube is fused to said optical fiber on opposite axial sides of said reflective element.

5. The industrial process control system of claim 1 wherein said sensing element comprises:

a tube fused to at least a portion of an optical fiber along a longitudinal axis of said tube;

a large diameter optical waveguide having an outer cladding and an inner core disposed therein; and

said tube and said wavguide being axially fused and optically coupled together.

6. The industrial process control system of claim 5 wherein said reflective element is embedded in said fiber and encased in said tube along said longitudinal axis of said tube.

7. The industrial process control system of claim 5 wherein said reflective element is disposed in said optical waveguide.

8. The industrial process control system of claim 1 wherein said material comprises a glass material.

9. The industrial process control system of claim 1 further comprising a housing attached to at least a portion of said sensing element which applies an axial strain on said sensing element due to said change in pressure.

10. The industrial process control system of claim 1 wherein said sensing element is strained in compression.

11. The industrial process control system of claim 1 wherein said reflective element is a Bragg grating, a laser, a DFB laser, or an interactive laser.

12. The industrial process control system of claim 1 wherein said reflective element has a characteristic wavelength and wherein said sensing element comprises a shape that provides a predetermined sensitivity to a shift in said wavelength due to a change in force on said tube.

13. The industrial process control system of claim 12 wherein said sensing element comprises a dogbone shape.

14. The industrial process control system of claim 1 wherein said sensing element comprises a dogbone shape and comprises an outer tube fused to at least a portion of large sections of said dogbone shape on opposite axial sides of said reflective element.

15. The industrial process control system of claim 1 further comprising a temperature reflective element disposed in said sensing element in thermal proximity to said pressurereflective element, and having a temperature reflection wavelength that changes with temperature.

16. The industrial process control system of claim 15 wherein said temperature reflection wavelength does not change in response to a change in said pressure wavelength due to a change in said pressure.

17. The industrial process control system of claim 1, further comprising an outer housing, surrounding said sensing element and suspension means disposed between said sensing element and said outer housing for suspending said sensing element within said housing.

18. The control system of claim 1 wherein said sensing element comprises a large diameter optical waveguide having an outer cladding and an inner core disposed therein and an outer waveguide dimension of at least 0.3 mm.

19. The industrial process control system of claim 18 wherein said processor further comnrises:

an optical instrument that provides a light signal to said pressure sensor and receives the pressure signal, wherein the pressure signal is an optical return signal; and

an opto-electrical converter receiving said optical output signal and converting said optical output signal into an electrical signal.

20. The control system of claim 1, wherein the device is one of at least a valve, a pump and a throttle.

21. A method for controlling the pressure of a fluid moving in a pipe of an industrial process, the method comprising:

providing an optical sensing element having at least one pressure reflective element disposed therein along a longitudinal axis of said sensing element, said pressure reflective element having a pressure reflection wavelength, at least a portion of said sensing element having a transverse cross-section which is contiguous and made of substantially the same material and having an outer transverse dimension of at least 0.3 mm;

axially straining said sensing element due to a change in pressure, said axial strain causing a change in said pressure reflection wavelength, and said change in said pressure reflection wavelength being indicative of said change in pressure;

determining the pressure of the fluid using said pressure signal; and

providing a control signal, in response to the determined pressure, to a device that controls a parameter that effects the pressure of the fluid within the pipe.

22. The method of claim 21, wherein the device is one of at least a valve, a pump and a throttle.

23. The method of claim 21 wherein said sensing element comprises:

an optical fiber, having said pressure reflective element embedded therein; and

a tube, having said optical fiber and said reflective element encased therein along a longitudinal axis of said tube, said tube being fused to at least a portion of said fiber.

24. The method of claim 23 wherein said tube is fused to said optical fiber where said reflective element is located.

25. The method of claim 23 wherein said tube is fused to said optical fiber on opposite axial sides of said reflective element.

26. The method of claim 21 wherein said sensing element comprises a large diameter optical waveguide having an outer cladding and an inner core disposed therein and an outer waveguide diameter of at least 0.3 mm.

27. The method of claim 21 wherein said straining step comprises axially compressing said sensing element.

28. The method of claim 21 wherein said reflective element is a Bragg grating, a laser, a DFB laser, or an interactive laser.

29. The method of claim 21 wherein said reflective element has a characteristic wavelength and wherein said sensing element has a shape that provides a predetermined sensitivity to a shift in said wavelength due to a change in force on said sensing element.

30. The method of claim 21 wherein said sensing element has a dogbone shape.

31. The method of claim 21 wherein said sensing element comprises a temperature reflective element disposed therein and in thermal proximity to said pressure reflective element, and having a temperature reflection wavelength that changes with temperature.

32. The method of claim 31 wherein said temperature reflection wavelength does not substantially change in response to a change in said pressure wavelength due to a change in said pressure.

33. The method of claim 21, further comprising a step of suspending said sensing element inside an outer housing.